PTC is shunted out shortly after initial power-up by a DC bus voltage sense circuit driving a relay rectifiers. The NTC is shunted out shortly after initial power-up by a relay driven by a DC bus voltage sense circuit. The sense circuit also controls the input autoranging selection relay on the autoranging MegaPAC. disabled to limit the inrush current, reduce peak currents in the autoranging relay contacts, and to allow switch or relay, a small capacitor should be connected between the control line and Signal Ground to www.datasheetarchive.com/files/vicor/vicor applications manual/000000/apps-man/apps_megapac_m.htm